The present invention relates to a method for producing a battery pack used as a power source for an electronic device, etc. and a battery pack produced therein.
Recently, a battery pack, which has an outer case of resin with a battery and a board mounting a protection circuit for preventing over-charging or over-discharging when charged or discharged, is used for a device such as a mobile phone, etc.
In such a battery pack, the battery and the board are mounted in the outer case, which is composed of an upper case and lower case, so as to be held conventionally. Recently, a low-temperature-mold resin is injected between the board and the battery or covers the battery to form molded resin. Such method is employed for reducing the number of parts and improving manufacturing efficiency.
Further, recently, external input-output terminals connecting the battery pack with an external circuit are not provided with lead wires but are formed on one surface of the board so as to be exposed to the outside, so that the battery pack is downsized.
On the other hand, generally, in manufacturing of the battery packs, the external input-output terminals should be accurately positioned at the relative position against the outer case or the mold resin. Thus, it is required that the board is retained against the battery previously when the low-temperature-mold resin is injected. In particular, the board is retained in position by a resin holder interposed between the board and the battery before the resin is injected, then they are molded with the holder together. Such method is also employed conventionally.
However, in this method, the holder interposed between them interferes with the flow of the resin during injection. Thus, the battery pack that is molded with the occurrence of the impaired flow of the resin may have cracks or pinholes in the inside or the outside of the molded resin. In such a case, the battery pack may have a problem such that an airtight connection between the board and the battery to be molded by the mold resin might not be achieved sufficiently, or sufficient mechanical strength might not be achieved. Such problems can reduce yield.
On the other hand, reducing the injecting velocity of the resin or increasing temperature of the resin or injecting pressure can reduce the occurrence of the impaired flow of the resin. However, it may cause other problems such as reduced manufacturing efficiency, or the battery or the protection circuit might be damaged.
Further, it is considered that employing resin material to be injected with low viscosity can reduce the occurrence of the impaired flow of the resin. However, the material having low viscosity at injection does into have sufficient mechanical strength as mold resin for the finished product.
The present invention has been developed to solve the above problems, and therefore, is aimed to at providing: a method for producing a battery pack with accuracy of positioning the external input-output terminals in high yield, without reducing manufacturing efficiency, and without increasing the number of the components; and a battery pack produced by the method.